In a nuclear reactor, moderators slow down the neutrons which come out in a fission process. The moderator used have light nuclei. Heavy nuclei will not serve the purpose, because:
1. | they will break up |
2. | elastic collision of neutrons with heavy nuclei will not slow them down |
3. | the net weight of the reactor would be unbearably high |
4. | substances with heavy nuclei do not occur in the liquid or gaseous state at room temperature |
(a) | nuclear forces have short-range. |
(b) | nuclei are positively charged. |
(c) | the original nuclei must be completely ionized before fusion can take place. |
(d) | the original nuclei must first break up before combining with each other. |